This protein prevents the prophage P22 c2 repressor protein from binding to its operators and also inhibits the action of other prophage repressor proteins, including those of phages lambda and 434. The synthesis of antirepressor is negatively regulated by the protein products of the two other immI genes, mnt and arc.

Involved in carotenoid biosynthesis. Antagonizes the transcriptional repressor proteins CarA and CarH by preventing their binding to DNA. Can also dissociate preformed CarA-DNA complexes. Does not bind DNA.